As the requirement of navigation and navigation update systems reach more exquisite accuracies, the stability of the optics, and of the optical detector themselves come to limit the ultimate accuracy of a system whose shelf life is prolonged. The purpose of a stellar updating device as applied to inertial platforms, is to locate a reference star (or stars) within the systems field of view and through knowledge of the location of the star in inertial space to use this information for taking out platform error of the inertial system accumulated during the hostile environment of launch or takeoff. The effect of telescope, sensor, or structure motion relative to the platform on which accelerometers are mounted will be an error in the output of a stellar update system. It would be desirable to calibrate out any changes in sensor or optics position and to perform the calibration just prior to use or to calibrate throughout the mission itself.
Present calibration techniques require the use of several mirrored surfaces and external autocollimators. Moreover, present calibration techniques do not permit pre-flight, in-flight or real time calibration. Since previous methods did not permit calibration directly before use, the optical tracker is susceptible to all slow instabilities in component mounting and electronics drift.